1. Field of the Invention
The present invention relates to the arrangement of an exposure apparatus used in an electrophotographic image forming apparatus in which a latent image formed by exposing a photosensitive member is developed and transferred to a recording sheet, thereby recording the image.
2. Related Background Art
An image forming apparatus is widely used in practice, in which light emitted by a stationary light source such as an LED array is focused onto the surface of a photosensitive member by using a focusing optical fiber lens array to form a latent image on the surface of the photosensitive drum, and the latent image is visualized with a toner and then transferred onto a recording sheet, thus forming an image. When an LED array is used as an exposure light source, the apparatus can be downsized more than in a case using a laser as the light source.
Particularly, a color image forming apparatus, which has three or four LED arrays and forms a color image by overlaying images corresponding to respective colors obtained by color separation, can utilize the advantage of downsizing obtained by using the LED arrays.
When, however, a color image is formed by overlaying three or four colors, if an overlay error occurs, color misregistration or color irregularity is produced to greatly degrade the image quality. More specifically, in the conventional exposure apparatus, even if the LED arrays are fabricated straight in the initial state, as the apparatus is operated and the temperature in the apparatus increases, the straightness gradually degrades. This is due to the following reason. As the temperature in the apparatus increases, the temperature of an LED head having the LED arrays also increases, and the LED head is distorted due to a difference in thermal expansion of the various types of members.
In order to solve this problem, a fan is provided to cool the LED head, so that the distortion of the LED head is suppressed. In this case, the size of the apparatus, power consumption, and noise disadvantageously increase.
Furthermore, in the conventional LED head, a foreign substance such as the toner or dust may enter through the gap between the constituent elements to attach to the light-emitting portion or image forming means. In this case, light is partly shielded to cause a defect in the image.